It is narrated from Sayyiduna Iyad bin Himar al-Mujashi'i (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever finds a lost item, let him make one or two upright men witnesses, and let him not conceal it nor hide anything of it. If he finds its owner, let him return it to him; otherwise it is the wealth of Allah, which He gives to whomever He wills."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12089